A flexible sensor device for moisture detection, a detecting method using the device, and applications of the device are disclosed. The flexible sensor device comprises a flexible sensing part (100) and a signal processing and transmitting part (200) which is connectable to the flexible sensing part (100), wherein the flexible sensing part (100) includes a non-conductive flexible substrate (110) and two or more conductive traces (130a, 130b) attached on a side face of the flexible substrate (110), wherein two conductive traces (130a, 130b) being not in contact with each other is chosen from the two or more conductive traces as a pair of conductive traces, the side face of the flexible substrate (110) which is provided with the conductive traces is a side face in direct contact with a surface to be detected, and the signal processing and transmitting part (200) has a detection module (240) for detecting the capacitance and resistance between the conductive traces (130a, 130b) of the pair of conductive traces so as to determine the moisture content of the surface to be detected.